Turkey's artillery shelled Islamic State group targets across the border in Syria for the second consecutive day on Tuesday, a senior Turkish official said, amid reports that Turkey-backed Syrian rebels were preparing an offensive against an IS-held border town in northern Syria.

The Ankara official said the Turkish shelling came after mortar rounds, believed to have been fired by the militants from the Syrian town of Jarablus, landed on Turkish territory. The official, who spoke on condition of anonymity in line with government regulations, did not provide further details.

Turkey has increased security measures at its border opposite the Islamic State-held Jarablus, deploying tanks and armored personnel carriers in recent days. Syrian activists have said that hundreds of Turkish-backed Syrian opposition fighters are gathered in the Turkish border area of Karkamis in preparation for an attack on Jarablus.

Ankara is concerned about the growing power of U.S.-backed Syrian Kurdish forces, who it says are linked to Kurdish groups waging an insurgency in southeastern Turkey.

In Syria, a Kurdish-led group known as the Syria Democratic Forces earlier this month liberated the nearby town of Manbij from the Islamic State group, triggering concerns in Ankara that they would seize the entire border strip with Turkey.

Jarablus is a vital supply line and the last border point that directly connects the Islamic State group with Turkey and the outside world, and separates Kurdish-controlled areas in northern Syria.

Meanwhile, a rebel commander affiliated with the SDF was killed shortly after broadcasting a statement announcing the formation of the so-called Jarablus Military Council and vowing to protect civilians in Jarablus from Turkish "aggression.''

Abdel-Sattar al-Jader was shot by unknown gunmen late Monday, an hour after reading the statement posted online in which he also accused Turkey of mobilizing fighters and ``terrorists'' through the border toward Jarablus. Al-Jader pledged to fight Turkish efforts to take control of the city and warned Ankara against further aggression. The SDF also issued a statement in which it declared its full support for the council.

The council, in a statement issued after his death, accused Turkish security agents of being behind the slaying. There was no immediate comment from Turkey.

The Hurriyet newspaper and others said the mortar rounds Tuesday hit the town of Karkamis, in Turkey's Gaziantep province. One of them exploded in the garden of a house, but no one was hurt.

Anadolu Agency said Turkish artillery fired 40 rounds against IS targets in retaliation, after three rockets fired from Syria landed into an empty field in the town of Kilis. The report says the Turkish Armed Forces "covered the area with fire'' without providing any details. No one was hurt by the rockets.

On Monday, Turkish artillery attacked a U.S.-backed Syrian Kurdish militia as well as IS positions in Syria.